This invention relates generally to electrophotographic reproduction devices and, more particularly, to an optical system for such a device which scans a document at an object plane and transmits the image to a moving photoconductive surface.
Conventional scanning systems for scanning a document placed on a transparent platen are exemplified by the system disclosed in U.S. Pat. No. 4,332,460. Typically, a photoreceptor drum or belt is driven in a desired direction, and at a desired speed, by an ac or dc drive motor via an associated main drive shaft. The rotary motion of the main drive shaft is transmitted into a lateral motion via a system of cables, capstans, pulleys and clutches, the lateral motion being then applied to the various optical components such as scanning mirrors and lamps generally via a carriage upon which the components are mounted. Each optical component, such as a full-rate or half-rate scan mirror, can be driven at separate rates of speed by selection of appropriate pulley diameters and cable lengths. The scan system then goes through cycles of document scan and rescan motions. During the scan cycle, each carriage is driven at a fixed speed ratio relative to the photoreceptor. For rescan, the drive direction is reversed and the scan components are returned to start of scan position, generally at an accelerated speed. Changes in magnification require different combinations of carriage/photoreceptor scan ratios, rescan speeds, and start of scan positions. In order to accomplish these various actions, and as is generally known in the prior art, a complicated system of electro-mechanical clutches and variable transmission ratios are required as exemplified in the referenced patent. These systems are difficult to design and, once designed for a specific system, are also difficult to modify. The components and their assemblies are costly and are subject to deterioration due to inevitable mechanical wear. Further, the acceleration parameters are restrained because of the slow response time due to the inertia of the carriage components.
The present invention is directed towards a scanning system wherein the translational motions of the scanning components are provided by a plurality of independently driven linear motors. Each of the linear motors cooperates with an associated carriage support structure upon which is mounted the optical element to be moved. Each motor is under the control of a master control system which synchronizes the scanning component movement with that of the photoreceptor and which, further, provides variable position and speed relationships among the scan components, the platen and the photoreceptor through a range of magnifications. The control system comprises a digital controller and amplifier for each linear motor and incorporates a feedback circuit to monitor motion acceleration velocity or position of the scan components.
More particularly, the invention relates to an optical imaging system for scanning an original document in an object plane and projecting an image at a selected magnification, onto a moving photoreceptor, the system comprising:
optical means for scanning and illuminating an original document to be copied, said scanning means including at least two moving scan components, each with a separate drive means to provide an independent rate of scan motion, said drive means including a linear electric motor,
projection means for projecting a light image from said document onto said photoreceptor, and
digital control means adapted to control the operation of said drive means in selected modes of operation.
According to a further aspect of the invention, the digital control means includes supervising control means to feed back acceleration, velocity and position signals of said moving scan components.